Par Eloise Aube
Posted on 14 Jul 23 at 8:56 See my news Follow 76news On the beach in Le Havre, like everywhere else, jellyfish are numerous. (©François Benard / DR)
Barely the toe put in the water that you watch if a jellyfish (or more) is nearby. A scenario that you have already experienced, right?
At Le Havre beach, in the summer season, it is not uncommon to come across them at sea or stranded on the sand. Some even say that these jelly-like marine animals are becoming more and more numerous. But the answer is not so clear. 76 currently takes stock of the subject.
When do jellyfish arrive on our beaches?
Generally, the breeding period of jellyfish takes place between April and May. It is possible to see some at this time until the end of the summer, as explained to actu.frDelphine Thibault, researcher at the Mediterranean Institute of Oceanology “They are visible at this time because food is available in the water. The wind conditions their appearance in certain areas because jellyfish organisms have little ability to move. So the sea currents bring them closer to the coast when the wind conditions are favourable”
However, in recent years, it is clear that jellyfish do not only land on sunny days, but also in winter.
This is explained to us by Chloé Dancie, research engineer within the Normandy Coastline Monitoring Unit.
In Normandy, in recent years, episodes of bloom [une croissance rapide de la population des méduses, NDLR] result in significant strandings on the coasts which reproduce cyclically during the summer, but in recent years, they have been increasing in number on a global scale and occur every year even in winter.
Chloe DancieNormandy Coastline Monitoring Unit
Concretely, it is possible to see jellyfish (almost) all year round on the beach in Le Havre although we observe more of them in the summer.
Why are there more?
It’s a fact: in recent years, jellyfish have been increasing in number (even if it is difficult, if not impossible, to have precise figures). Not only in the Mediterranean but also on the beaches of Normandy.
Videos: currently on Actu
What is it due to? Difficult to have a definite answer so explanations are multifactorial.
First, it can be eutrophication, in other words a natural form of pollution “which occurs when the environment receives too many nutrients that can be assimilated by algae and that they proliferate”, specifies the CNRS. It can also be “the variability of currents and winds”, notes Chloé Dancie.
Overfishing, the disappearance of certain predators or the modification of certain habitats are all hypotheses put forward to explain this proliferation.
sea temperature
The successive hot spells of recent months – with a record month of June – can also explain the multiplication of jellyfish.
Because these gelatinous little beasts love hot water. For example, the Chrysaora hysoscella (called the compass jellyfish that we regularly see in Le Havre) supports maximum temperatures of between 28 and 32°C.
Jellyfish species tolerate a wide temperature range but an increase in temperature can lead to increased blooms by promoting growth and egg production of jellyfish.
Chloe Dancieresearch engineer at the Normandy Coast Monitoring Unit
Blame it on global warming?
And the global warming in all of that ? Once again, the answer is not settled within the scientific community.
And the expert concludes: “We cannot make a link between the arrival of jellyfish on the beaches of Le Havre, and global warming. Jellyfish populations are on the rise all over the world, but the reason is surely a combination of several abiotic, biotic and anthropogenic factors, including global warming.
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